Under your Skype settings | Audio Settings, make sure that the appropriate Microphone input device is selected. The Volume meter should also bob up and down as you talk when the Settings window is open. Keep selecting different devices until you see movement on that meter.

You can test your audio settings by calling the Echo / Sound Test Service (Skype name "echo123") that should be in your Skype address book. No need to bug your friends while you troubleshoot.

On skype clik tools then click audio setting then click arrow for microphone and test sound for each line in I had same trouble just have to get the right mike line in and works fine except I have to do it everytime I reboot and also have to do that to get mike working on messenger